What legal basis is there for a car to behave differently during an emissions test? Its not like it has to machine learn which jurisdiction its in to tune its

What legal basis is there for a car to behave differently during an emissions test? Its not like it has to machine learn which jurisdiction its in to tune its emissions, they know which region its going to be sold in and can make the appropriate settings. Even if some sort of detection were needed the emissions test isn't your key as not every car undergoes it, only a sample.